Make sure you have the Mastermind Badge! You gain this after you have defeated Meowiarty in Big Ben. After that, speak to Watson and Sherlock Bones inside the Royal Museum. They will direct you to Headmaster Ambrose. Ambrose will then give you a spiral key to MooShu, where Su Lee will greet you!
If you have done this already, you may want to contact Wizard101 support. They will refresh your quest line.
